I just keep it in a bucket of saltwater (mixed from tap water since my tap water source has a lot of nitrates). Keep it near a window where it'll get sunlight. It'll stay alive even with temperature swings. Usually I wait until someone local needs some and I just give them a ton.
You might want to consider investing in a composting bin. I would love to get one myself but I don't have the room.There must be a use for this stuff. My first thought was squeezing it like wheatgrass and taking shots. But that also sounds disgusting.
Seriously, what can one do with waste chaeto?